Last week the city of Vancouver proposed building a subway line to replace the 99 B-Line bus. This TransLink route carries over 160,000 people per day, making it by far the busiest bus route in North America (by comparison, New York's busiest bus route, the M15, carries 55,000 daily passengers). It is a perfect case study of upgrading a successful transit line to a higher capacity technology, for the situations where you just can't run enough buses to keep up with demand. Going back to an earlier post on vehicle selection, we see that rail vehicles hold more people than buses.
|Transit Bus (40 feet)||35 seats, up to 65 total ("crush load")|
|Articulated Bus (60 feet)||57 seats, up to 85 total ("crush load")|
|Light Rail (70-100 feet)||100 per car, up to 4 cars|
|Subway||150-200 per car, up to 10 cars|
Experience with bus bunching shows us that things start to break down when you're running service every 5 minutes or less. It's very difficult to manage the service in a way that keeps buses spaced out, and as you add more buses they just become more crowded and the bunching gets worse. This can happen with rail as well, worsened by the inability for vehicles to pass each other. (On the trunk portion of Boston's Green Line and New York's subway, for example, every 10-second delay cascades down the line.)
That's when you know it's time to increase capacity. You can run long high-capacity trains with one operator. Surface light rail is usually the way to go, but because ridership grows with a jump in the quality of service (and the 99 B-Line ridership is already so high), Vancouver is right to build a subway. Hopefully they can convince the province and federal government to help pay for it.